An Accidental Genocide
by UnleashThePuns
Summary: A young Frisk is new to the Underground and is already enjoying their time there but when Toriel goes on ahead to get everything for the surprise of cinnamon-butterscotch pie things go terribly wrong. After accidentally killing a Froggit, Frisk is taken over by Chara who wants revenge for what the monsters did to her. When they reach the Judgement Hall will Sans realize the truth?
1. Chapter 1

**Undertale is owned by Toby Fox and not by us.**

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Chapter 1

A young person/whatever/determination by the name of Frisk headed up Mt. Ebott on their own for a reason currently unknown other than wanting to see if the stories about monsters are true. As the determination **(AN: Determination is one of Frisk's gender pronouns in this fic)** climbed up the mountain and found the giant hole in the ground, they paused for a moment; a butterfly fluttered past, capturing the rather tiny child's attention before they looked back at the entrance to the unknown.

They tentatively began to move forward when the butterfly came into their vision again but moments later they glanced down into the opening at their feet. A blanket of yellow was at the bottom, sparking their curiosity. The young determination reached forward to try to grab onto the butterfly that moved backwards out of their grasp before the child took a few steps back then ran forward, jumping after the small insect. Their hands closed around it, unknowingly the child ruined its ability to fly, as they began to fall towards the yellow blanket.

Once they landed Frisk realized that the yellow blanket was in fact soft flowers that broke their fall. In their hands they still held the butterfly and they looked at it closely, admiring the beautiful wings before noticing a small tear. It would no longer be able to fly… but on the bright side Frisk has a new pet! They plopped the disabled butterfly onto their tiny shoulders and examined their surroundings. They noticed an entryway with tall white poles surrounded by more flowers. Frisk stood up slowly and made their way to the rest of the mountain. They came upon another room and a soft, bouncy music began to play. In the new room was a single spotlight, which was showcasing a small, yellow flower. However, this flower was bigger than the others that Frisk had encountered, and it seemed to even have a face. How odd.

"Howdy! I'm Flowey, Flowey the- Hey! What are you doing?"

Frisk gave a cheesy little grin as they reached over to the flower that was now right in front of them. They plucked Flowey out of the ground and started playing with the petals. Flowey scrambled to get out of their grasp, but they wouldn't budge. Toriel hears Flowey screaming profanities and rushes over, preparing to help the small child from the demented plant, but stopped short. Apparently the roles were quite reversed and she looked very confused.

"Child..? What is going on here?"

"THIS DEMON GIRL IS-"

Frisk grabs a petal threateningly, "I no giwl! I detewmination!"

"You're not what, you insane candy cane?" Flowey the flower was not a happy camper. Toriel… was a very confused goat who is about to intervene when Frisk, the apparent determination, got up and ran over to her, carrying Flowey in their hand and a butterfly on their shoulder.

"He-Hello young one… what is your name?"

Frisk grinned proudly up at her, deciding instantly that they like the goat and will forever call them their goat mom. "Fwisk! And this is Buttew! He no able to fly so he no a buttewfly."

~~~~~~~~~~~~~~~~~~~~~~~~Time Skip!~~~~~~~~~~~~~~~~~~~~~~~~

After having Frisk walk down the hall without her, Toriel finally managed to get Flowey away from the self-proclaimed determination and set him on the ground. For once she took pity on the flower being held captive by the striped shirt child and so she freed him, watching as he disappeared into the ground.

"Now… Frisk, I apologize for this but I must go get something ready back at my home. Stay here, young one and I will be back soon. Here is a cell phone that you may use." Toriel handed Frisk the old, ancient cell phone and left after getting an 'okay goat mommy'.

After a few minutes alone Frisk decided to call Toriel and try to flirt with her yet the cuteness of them not being able to pronounce any 'r's caused an 'awww' and laughter from the goat-like monster. Eventually, Frisk got restless and went to explore the ruins. Along the way, they were approached by Froggit, who they decided would be fun to play with.

The two decided to play-fight, neither imaging how wrong it could go. Butter was set on the ground to watch them and be the referee of the play-match. Frisk was playing with their 'sword'(stick) and Froggit with his own usual attacks, but more carefully as to not hit the child, when Frisk tripped and hit Froggit with their full strength, causing actual damage to the monster. Frisk and Butter watched in horror as Froggit frowned and began to turn to dust.

Unknown to them, there was a spirit watching them closely. A young girl by the name of Chara who was waiting for Frisk to kill a monster. That time was now and it left an opening for her to take them over.

"Ah, much better. Having an actual body now makes it much easier to kill them all myself rather than have that stupid flower do it for me."

She picks up Butter and sets him on her shoulder, grinning wickedly. Frisk was currently stuck inside their own mind; forced to watch all the terrible deeds that Chara will do.


	2. Chapter 2

Chapter 2

Chara makes her way steadily through the underground, a twisted grin on her face and red eyes shining through the darkness. Dust from dead monsters was starting to cover her hands, but for now she manages to keep it off her clothes. How else would she keep Toriel, her old mother, from knowing that all the monsters were dead until she kills the goat as well? Of course, she doesn't care much if Toriel figures out that the monsters are dead right away, the boss monster's life will end soon enough. She mostly just doesn't want dust on her clothes from such weak, stupid monsters.

But w-why would you kill goat mom?! Wa-Wasn't killing all th-the othew cute monstews enough?!

"No! It's never enough! Not after what they all did to me!" Chara screeches, causing a stray monster to jump out of its hiding place. She grins wickedly and pulls out her knife, slowly walking towards the monster. In one swipe, they turn to dust and Chara dusted off her sweater, "They'll all die, and if I get my way, they will die again and again and again. Forever!" She won't let a single monster live, no matter what. In fact, she even goes to the spider bake sale and kills the spiders before taking a couple donuts and cider for along the way. Although she would much rather prefer pie.

All the monsters in the Ruins were soon dead, besides the area's boss monster. Dust was scattered throughout the rooms, the only hint that there had once been living beings there. As she keeps going through the Ruins, she would sometimes teasingly call out for more monsters.

But nobody came.

Frisk was sobbing and pleading silently in the back of their shared mind, making the evil one in control cackle maniacally in glee, glad that she can so easily make them cry.

Chara was now getting close to her soon to be dead mother's home. As she approaches the tree, her phone rings and she sees Toriel out of the corner of her vision before the mother figure ran over.

"My child! There you are! I should not have left you alone for so long like that, I apologize. Please, come in. You may take a nap in this room and there will be a surprise when you wake up." Toriel takes Chara's hand, thinking she was Frisk, and leads her inside and to a simple bedroom. There was a box of uninteresting toys, an empty picture frame, and other items that showed that the room is meant for a child. It nearly reminds Chara of another room, long ago, but she doesn't think much on it. Instead she let a sick, evil grin form on her face as she ran her fingers lightly over the blade of her knife.

"Thank you, mother. I suppose I shall now take a nap."

Toriel looks at 'Frisk' in confusion, wondering why the human child had spoken so formally, only to be met with bright red eyes, an evil grin, and a green striped sweater that occasionally glitches back to Frisk's usual purple one. Toriel jumps back and frantically moves as far away from Chara as possible, horrified at the sudden reappearance. As she shoots her magic fire at the child in defense, Chara simply dodges them one by one, and walked calmly over to Toriel, her sick and twisted grin still in place. With plastic knife in hand, she attacks Toriel, killing her with one swift slash. Frisk watches Toriel fall and they scream and cry in horror, wishing and begging for Chara to stop but was simply told to shut up by the girl in control of their body.

Her mother figure is now dust on the floor of the bedroom meant for the young human. Chara felt a sense of sick nostalgia as she walks through the house and heads for the kitchen, noticing a fresh cinnamon-butterscotch pie; her old favorite and so much better than the spider goods she took. Chara takes the entire pie and heads toward the exit of the ruins, a slight bounce in her step from feeling excited over killing more monsters.

"It's not like there's anyone here to eat it anymore." She smirks and takes a piece out to eat, the familiar taste washing over her tastebuds and almost bringing a normal, genuine smile to her lips. Almost. It is just a pie, all it can do is remind her of memories that she pushes away without a second thought. She doesn't need memories of those times, they are long behind her. As far as she is concerned, they are somebody else's memories instead of her own. They mean nothing to her now and she will destroy every last monster in the Underground no matter what.

 **Next up… is Sans.**

 _Who Sans? What you going to do to him?_

 **You'll see, string bean. The old comedian's got it coming and best way to get him is through his idiot brother.**


	3. Chapter 3

Chapter 3

Soft footsteps can be heard as Chara leaves through the door that Toriel had originally been planning to destroy before she was killed. The demented girl finds herself in another room, in which her old partner, Flowey, sprouts up from the ground. The yellow flower at first thinks the child is still Frisk before noticing the red eyes and glitching green clothes.

"Chara! So the brat killed a monster, huh? That's dandy!" Flowey erupts into laughter, the mere thought that the child who had threatened to pull his petals was now under Chara's control seemed hilarious to him.

"Enough laughing," Chara interrupts sharply, "We have business to discuss." Her knife glistens with dust and Flowey visibly gulps, which seemed pretty impossible for a flower, but he manages.

"W-what business? We're going to work together to destroy the monsters, aren't we?" Flowey doesn't seem nearly as amused or confident as just a moment ago.

"Oh, Asriel… how naive." Chara glitches and her deadly grin seemed to brighten, "My business proposal is this… you stay out of my way, and your stupid little life might just survive if you're lucky. I'm sure you know what will happen if you aren't so lucky. You understand, my incompetent little flower?"

Almost immediately a nod came from the soulless flower, intimated by the girl who had once upon a time been his sister and partner, "Ye-Yes Chara…" For once, he actually felt fear and he could not remember the last time he had felt something so strongly. The girl flicks her wrist, the knife centimeters in front of his face, dismissing the flower in a movement that showed how she could have sliced him easily without a second thought.

Once Flowey disappears back into the ground, Chara begins moving forward once more until she was outside. Snow covered the ground and there were trees on either side of her, a chilly breeze barely going noticed by the killer.

A small stick snaps beneath her feet but she paid no attention to it, having heard the same crack all those times before. As she approaches a short bridge with bars that had a too wide gap between them, she hears footsteps behind her. Before anything could be said she turns around, coming face to well chest, until she looks up at their face, with a familiar skeletal grin from the lazy comedian known as Sans.

Chara let an innocent smile come to her face and she made sure she wasn't glitching. Wouldn't want the dumb comedian to know that something's up, right? Ah well… she does but not until he couldn't do anything. She doesn't listen to him joking with her, telling her about how his brother is a human hunting fanatic but as she hears Papyrus yell Sans' name from way up ahead, she lets herself glitch.

The skeleton seems surprised before his left eye turns blue with magic, his other darkening to pure black as he spoke, "So, kid, you aren't a human then, are you? By the looks of it you've already gained some L.O.V.E., and I should rip your little throat out right now but-" "SANS!" Interrupts Papyrus' voice as he gets closer, making the shorter skeleton immediately make himself look calm and collected, stuffing his glowing hands into his jacket pockets and letting his glowing eye turn back to normal, "-if you hurt Paps you'll have a really bad time." He whispers to Chara before turning his attention to his younger yet taller brother. Chara quickly hides in the bushes and waits for their conversation to begin.

"SANS, YOU LAZY BONES, WHAT ARE YOU DOING AWAY FROM YOUR STATION?!"

"Oh, hey bro." Sans chokes out in his usual 'cheery' voice, "I'm just on break."

"SANS YOU TOOK A BREAK JUST HALF AN HOUR AGO."

"No, that was my lunch break."

"YOU TOOK YOUR LUNCH BREAK TWO HOURS AGO."

"Oh well."

"SANS."

"Calm down, Papyrus. You wouldn't want to work yourself.."

"DON'T"

"Down to the bone!" Sans gives a cheeky wink and Papyrus face-palmed. In Chara's head she can hear a slight, weak giggle from Frisk at the pun, though she knows that the child will not be able to even weakly giggle for long after watching more monsters be killed. Chara then uses the opportunity to sneak behind Papyrus. Sans was joking with his brother when he sees Chara behind the taller skeleton, or Frisk, or whoever, it was hard to tell when the 'determination' was constantly glitching and switching between Chara's beady red eyes and Frisk's innocent, scared gaze. Sans could feel his bones heat up with the power of his magic, but tries his best to keep his eye at bay for Paps' sake.

Chara grins and walks a step closer to Papyrus, taking out her trusted, dusty knife. Sans takes a step closer to Papyrus as well and shoots a quick threatening look to Chara, all while thinking of a pun out of mid air to keep the conversation going. Each time she takes a step, so does he. Finally, Chara jumps forward and Sans gives in. His eye starts to glow and he grabs Chara and slams her against a tree.

"SANS?" Papyrus looks back to find nothing and turns to Sans with a confused look on his face, "WHAT WAS THE GLOWING EYE THING ABOUT? I'VE NEVER EVEN SEEN YOU DO THAT! WOWIE!" Sans shrugs and dismisses his brother's questions.

"Hey Paps, I'm gonna go to Grillby's. Wanna join?"

"NO THANK YOU BROTHER, SOMEONE HAS TO KEEP WATCH FOR HUMANS!"

Sans waves a goodbye then turns to the opposite direction of Snowdin and walks behind a tree. He snaps his fingers and he feels himself teleport to the entrance of Grillby's. Chara watches as he leaves before returning to walking down the path until she runs into the taller skeleton who had walked off to return to his own sentry station.

 **This could be rather fun, the comedian already doesn't trust us so he'll be even more pissed when I kill his brother.**

N-No! No huwt him! He seem weally nice!

But young Frisk was ignored. Papyrus had turned around and was now staring at the human, mouth open in surprise as he realizes what they are.

"WOWIE! A HUMAN! I SHALL CAPTURE YOU AND BRING YOU TO UNDYNE WHO WILL BE SO IMPRESSED WITH I, THE GREAT PAPYRUS, AND MAKE ME A MEMBER OF THE ROYAL GUARD! THEN I WILL BE POPULAR AND FINALLY HAVE FRIENDS! PREPARE TO- HUMAN, I MUST ASK WHERE IT IS YOU ARE GOING, IT IS RUDE TO WALK PAST SOMEBODY AS THEY ARE SPEAKING, IS IT NOT?"

Chara paid no heed to Papyrus for now, knowing she will easily murder him soon enough. She walked past him and kept going, ignoring all of his puzzles until they reached a town that seemed to be deserted. The murderous girl stole a couple Cinnamon Bunnies to quickly snack on just because even she has to admit that they're good, before meeting a monster child with no arms who spoke about Undyne, going on and on about how amazing and cool the head of the royal guard was along with how the rest of the townsfolk are idiots for running when they know that Undyne will save them. It was all Undyne this, Undyne that, on and on about her. That's the second time Chara's heard that name and she grinned, remembering when Undyne had been younger and being trained by Asgore.

 **So Undyne is leader of the royal guard now, huh? Can't wait to fight her, see if the dumb fish will actually put up a fight unlike the rest.**

It wasn't long until Chara was heading past Sans and Papyrus' house and out of Snowdin where she could barely see the shadow of the taller skeleton in front of her but she was suddenly able to see him better.

"HALT, HUMAN!"


End file.
